Material for electrophotographic purposes



United States Patent Martha Tomanek, Wiesbaden-Biebrich, Germany, assignor, by mesne assignments, Murray Hill, NJ. N Drawing. Filed Oct. 10, 1963, Ser. No. 315,391 Claims priority, application Germany, Oct. 13, 1962,

47,966 53 Claims. (Cl. 96-15) Electrophotographic material, as isknown, comprises a support having a photoelectrically conductive insulating layer thereon, the layer containing a semiconductor compound. This layer is electrostatically charged, in the dark, and is then image-wiseexposed, either under a master or'by episcopic means, thus producing on the photoelectrically conductive layer a latent electrostatic image which corresponds to the master used. This image is developed by briefly contacting it with a resin powder, a visible image being produced by adherence of the resin to the charged areas. The image is fixed by heating or by the action of solvent vapors; by this treatment, the resin powder is anchored to the support and can not be rubbed off.

Inorganic substances, such as zinc oxide, have already been used as photo-semiconductor compounds. Organic substances, such as anthracene, anthraquinone, benzidine, oxadiazoles, and triazoles, have also been employed for this purpose. The known photo-semiconductor compounds are light-sensitive particularly in the near ultraviolet region. In general, this requires special precautionary measures during imageproduction.

The present invention provides a material for electrophotographic purposes, comprising a support and a photoelectrically conductive insulating layer, in which the photoelectrically conductive insulating layer comprises one or more thiodiazoles of the general formula to Azoplate Corporation,

in which R and R are similar or dilferent residues and may be hydrogen, a straight-chain or branched-chain aliphatic hydrocarbon residue, or a saturated carbocyclic or heterocyclic residue; R is an aromatic hydrocarbon or heterocyclic residue, which may be substituted.

The compounds of the present invention are particularly suitable for all electrophotographic purposes, since the light-sensitivity thereof in the visible region of the spectrum is considerably higher than that of known organic photoconductors. In addition, the present compounds are excellently suitable for the purpose of photoelectrically conductive insulating layers which, due -to their improved homogeneous constitution, favorably distinguish from known insulating layers. The compounds are colorless or light yellow and possess desirable photosemiconductor properties. Images with sharp lines and contrasts may be producedby the electrophotographic process using this material.

The residues R and R in the above general formula may represent hydrogen, or a straight-chain or branchedchain aliphatic hydrocarbon group, e.g. methyl, ethyl, propyl, isopropyl, butyl, hexyl; or a saturated carbocyclic radical, e.g. cyclopentyl, cyclohexyl, 2,4-dimethylhexyl; or a heterocyclic radical, e.g. tetrahydrofuryl, or a piperazine or morpholine residue. R may stand for an aromatic hydrocarbon group, e.g. phenyl, diphenyl-naphthyl, a pyrene, phenanthrene, 'indene, anthracene,- perylene or fluorene residue, or an aromatic heterocyclic group, e.g. a furane, thiophene, pyrolypyridine, or indole residue.

The aromatic hydrocarbon groups and heterocyclic 3,390,987 Patented July 2, 1968 groups designated by R, also may be substituted. Suitable substituents are preferably the amino and monoand dialkylamino groups; halogens; alkyl groups, such as methyl, ethyl, and propyl groups, and alkoxy and carbalkoxy groups.

-It is preferred that the amino group or monoor dialkylamino group represented by R be in the para position to the C-atom linked to the thiodiazole nucleus.

Particularly good photo-semiconductor properties are obtained when the compound corresponding to the present invention has a symmetrical constitution, i.e. when the R substituent corresponds to the substitucnt in the R position.

Exemplary of the compounds to be employed in the present invention are those of the following structural formulae:

Formula 15 Formula 16 i ii-G-monrm Formula 17 @at a Mt c S Formula 18 ll ii Formula 19 I I-1 t /CHz-CH, s CHPCIIZ Formula 20 N-N orrPoH,

II II s Gin-CH,

Formula 21 Formula 22 The foregoing exemplary compounds are:

2,5 -bis- [4-diethylamino-phenyl- 1 l, 3,4-thiodiazole (Formula 1),

2,5-bis-[4'-di-n-propylamino-phenyl-(1')]-1,3,4-

thiodiazole (Formula 2),

2,5-bis-[4'-ethyl-n-propylamino-phenyl-(1') ]-1,3,4-

thiodiazole (Formula 3),

2,5 -bis- [4'-n-propylamino-phenyl-( l) -1 ,3,4-thiodiazole (Formula 4),

2,5-bis-[4'-isoamylamino-phenyl-( l')]-1,3,4-thiodiazole (Formula 5),

2,5-bis-[4'-ethylamino-phenyl-(1') ]-l,3,4-thiodiazole (Formula 6),

2-phenyl-5-[4-diethylamino-phenyl-(1')]-1,3,4-

thiodiazole (Formula 7),

. 4. 2-[4-chloro-phenyl-(1) ]-5- [4"-diethylamino-phenyl- (l")]l,3,4-thiodiazole (Formula 8),

2- [4-methoxy-phenyl-( 1) ]-5- 4"-di-n-propylaminophenyl-(1")]-1,3,4-thiodiazole (Formula 9), 2-[4'-methoxy-phenyl-(1') ]-5- [4"-dimethylamino-phenyl- (l")]-1,3,4-thiodiazole (Formula 10), 2-phenyl-5- [4'-dimethylamino-phenyl-( 1') ]-1,3,4-

thiodiazole (Formula 11), 2-[4'-bromo-phenyl-( 1') ]-5-[4"-diethylamino-phenyl- (1")]-l,3,4-thiodiazole (Formula 12), 2-[2-to1yl- 1') ]-5-[4"-diethylamino-phenyl-( 1") ]-l,3,4-

thiodiazole (Formula 13), 2-[naphthyl-( 1 -5- [4"-diethylamino-phenyl-( 1") ]-1,3,4-

thiodiazole (Formula 14), 2-[furyl-( 1 ]-5- [4"-diethylamino-phenyl- (1") ]-l,3,4-

thiodazole (Formula 15),

2- pyridyl- (4) ]-5-[4"-diethylamino-phenyl-(1") ]-l,3,4-

thiodiazole (Formula 16), Z-phenyl-S-[4-isoamylamino-phenyl-(1")]-1,3,4-

thiodiazole (Formula 17), Z-phenyl-S-[4"-ethylamino-phenyl-(1") ]-1,3,4-

thiodiazole (Formula 18), 2-phenyl-5-[4'-cyclopentylamino-phenyll') ]-l,3,4-

thiodiazole (Formula 19), 2-pheny1-5- [4-cyclohexyl-arnino-phenyl-(1) ]-1,3,4-

thiodiazole (Formula 20), 2-phenyl-5-[4'-n-butyl-amino-phenyl-(1) ]-1,3,4-

thiodiazole (Formula 21), 2-[3'-chloro-phenyl-(1) ]-5- [5-diethylamino-phenyl- (1") ]-1,3,4-thiodiazole (Formula 22) The thiodiazole compounds may be used in admixture with each other or with other photoelectrically conductive substances. The photosemiconductors according to the present invention are advantageously prepared in accordance with the procedure of copending application Serial No. 315,389, filed Oct. 10, 1963, now abandoned.

According to the procedure of the copending application, supra, the thiodiazoles may be prepared 'by condensing two moles of an aromatic carbocyclic acid with one mole of hydrazine sulfate in the presence of phophorus sulfides, such as phosphorus pentasulfide (P 8 and/or phosphorus trisulfide (P 8 and/ or phosphorus heptasulfide (P 8 and in the presence of a base having a tertiary nitrogen atom, such as pyridine, methyl pyridine, quinoline, methylquinoline, N-methylpiperidine, or dialkyl aniline. Condensation is effected at temperatures exceeding C., and the reaction time is from 3 to- 5 hours. The reaction mixture is then poured into water, rendered alkaline with caustic soda solution, the base is removed by steam distillation, and the residue is filtered and dried.

By this process, symmetrically substituted thiodiazoles are obtained.

Unsymmetrical thiodiazoles are prepared by condensing one mole of a monoacyl hydrazine Ar CONHNH and one mole of a corresponding aromatic carboxylic acid in the presence of phosphorus sulfides with a base having a tertiary nitrogen atom, e.g. pyridine, and methylpyridine. Condensation in this case is also effected at temperatures exceeding 100 C., advantageously at C., and the reaction time is from 2 to 5 hours. Further processing of the reaction mixture is as in the case of the symmetrical thiodiazoles.

Exemplary of suitable supports for the photoconductive layers of the present invention are: metal foils, such as foils of aluminum, zinc or copper; cellulose products, such as paper or cellulose hydrate; cellulose esters, such as cellulose acetate or cellulose butyrate; or synthetic materials, such as polyolefins, e.g. polyethylene or polypropylene; polyvinyl compounds, such as polyvinyl chloride, polyvinylidene chloride or polystyrene; polyaerylic compounds, such as polyacrylonitrile or polymethacrylate; polyesters, such as polyterephthalio acid esters, and polyamides and polyurethanes.

If paper is to be used as the support, it should be pretreated to'prevent the penetration of coating solutions.

Metal-laminated films or films provided with a metal layer, e.g.-an aluminum layer, by vacuum deposition, are also suitable for these purposes. 1

For the preparation of the electrophotographic material, the photoconductive compounds according to the present invention are advantageously dissolved in organic solvents, such as benzene, acetone, methylene chloride or ethyleneglycol monomethyl ether, or in mixtures ofsuch solvents, and the solution is coated on a support in the customary manner, e.g. by immersion, spraying, brushing or by roller application. Further, it is often of advantage to use the compounds in admixture with organic resins as photoelectrically conductive layers.

Resins of this type are, for example: balsam resin, colophony, shellac and synthetic resins, such as colophony-modified phenol resins and other resins of which colophony constitutes the major part, coumarone resins,- indene resins, and the substances coming under the collective term synthetic lacquer resins. As shown in the Kunststoff-Taschenbuch (Plastics Pocket Book) by Saechtling-Zebrowski, 11th edition (1955), pages 212 et seq., these synthetic lacquer resins include: modified natural substances, such as cellulose ethers, polymerides such as vinyl polymerides, e.g. polyvinyl chloride, polyvinyle idene chloride, polyvinyl acetate, polyvinyl acetals, and polyvinyl ethers; interpolymers of vinyl chloride, vinyl acetate, and maleic acid; polyacrylates and polymethacrylates; polystyrene and copolymers of styrene, e.g. of styrene and maleic anhydride; isobutylene; chlorinated rubber; polycondensates, e.g. polyesters, such as phthalate resins, alkyd resins, and maleic resins; maleic acid-colophony mixed esters of high alcohols; phenol-formaldehyde resins, in particular colophony-modified phenol-formaldehyde condensates; urea-formaldehyde resins; melamineformaldehyde condensates; aldehyde resins; ketone resins; xylene-formaldehyde resins; polyamides; and polyurethanes. Further, phthalic acid esters, such as terephthalie and-isophthalic acid ethylene-glycol polyesters, and polyolefins, such as lower molecular weight polyethylene, may be used for this purpose.

When the compounds according to the present invention are used in admixture with the resins described, the proportion of resin to photoconductor compound may vary within wide limits. Mixtures in the range of two parts by weight of resin and one part by weight of photoelectrically conductive compound to one part by weight of resin and two parts by weight of photoconductor are to be preferred. Particularly good results are obtained by the u" of mixtures in a proportion of about 1:1, by weight.

Solutions of the compounds, if desired in admixture with resins, are applied to supports in known manner, e.g. by brushing, roller application or by spraying, and then dried, whereupon a uniform, homogeneous, clear, generally colorless, photoelectrically conductive layer is formed. The light-sensitivity of the photoconductive layers is in the range of short-wave visible light to the long-wave ultra-violet region, and, consequently, good results can be obtained with very short exposure periods even when light sources are used the main emission range of which is not in the ultra-violet region. However, the spectral sensitivity of the photoelectrically conductive layers may be shifted into the visible region of the spectrum by the addition of sensitizers, so that even shorter exposure times can be employed with good results. Even small additions, e.g. less than 0.01 percent by weight, show good effects. Such sensitizers, most of which are dyestuffs, are disclosed in Belgian Patent No. 558,078.

For the preparation of copies using the electrophotographic reproduction material of the present invention, an electrostatic charge is applied to the photoelectrically conductive insulating layer, e.g. by means of a corona discharge from a charging device maintained at 6000 to 7000 volts. The electrophotographic reproduction material then is exposed to light, either in contact with a master or by episcopic or diascopic projection of a master, so that an electrostatic image corresponding to the master is formed. This invisible image is developed by contacting it, in known manner, with a developer comprising a carrier and a toner. Alternatively, the developer may comprise a resin or a pigment suspended in a dielectric liquid. The image thus rendered visible in fixed, for instance by heating to about l0O-l70 C., preferably to 120i50 C, with an infrared radiator, or by treatment with solvent vapors, e.g., of trichloroethylene, carbon tetrachloride or ethyl alcohol, or with steam. Images are thus obtained which correspond to the masters used and which exhibit good contrast effect.

After fixation, the electrophotographic images thus ob tained may be converted into printing plates, by wiping over the support, e.g. paper or metal, with a solvent for the photoelectrically conductive layer, viz. with alcohols, such as methyl alcohol, ethyl or isopropyl alcohol, or ethyleneglycol monomethyl ether; with ether, such as dibutyl ether; or with mixtures of solvents. Acids, such as phosphoric acid; alkalies, such as sodium hydroxide; alkali phosphates, such as sodium phosphate; and silicates, such as sodium silicate; may be added to the solvents. Organic, alkaline-reacting substances may also be used for this purpose.

Suitable organic alkaline-reacting substances are primary, secondary and tertiary lower saturated amines, such as trimethyl amine, ethyl amine, diethyl amine, propyl amine and octyl amine; further, piperid'ne, N-methylpiperidine, morpholine, and amino alcohols, such as ethanol amine, and diethanol amine; diamines and polyarnines, e.g. ethylene diamine, triethylene tetramine, as also lower substituted acid amides, such as dimethyl formamide may be used.

After removal of the layer from the image-free areas, the entire surface is wiped over with water and inked up with greasy ink in known manner. In this way, printing plates are obtained which can be set up in an offset machine and used for making prints.

If a transparent support is used, the electrophotographic images obtained may be used as masters for the further production of copies on any light-sensitive layers. In this respect, too, the photoconductive compounds of the present invention are superior to the substances hitherto used, such as selenium or zinc oxide, since the latter yield only cloudy layers.

When a transparent support is used for the photoconductive layers, images may also be prepared by the reflex process. The electrophotographic material of the present invention has the advantage that it may be charged po itively as Well as negatively, so that positive images may be prepared from negative as well as from positive masters by simply reversing the polarity of charge, while the layer and the developer used remain the same. If, for instance, the layer is negatively charged and then exposed under a positive image, positive images are obtained when using a developer containing a positively charged toner. The toner carrying the positive charge deposits on the non-exposed, negatively charged areas.

When a positively charged layer is used, positive copies can be obtained, under identical conditions, from negative masters. In this case, the posi ively charged toner is repelled by the unexposed, positively charged areas and settles on the exposed, discharged areas.

The invention will be further illustrated by reference to the following specific examples:

Example 1 1 part by weight of 2,5-bis-[4'-diethylamino-phenyl- (1')]-l,3,4-thiodiazole (corresponding to Formula 1) and 1.2 parts by weight of a polyindene resin having a softening point of C. (Gebagan resin J/T 80) are dissolved in 30 parts by weight of chloroform and 0.002 part by weight of crystal violet, dissolved in 0.5 part by volume of methanol, is added to the solution. This solution is then applied to paper, the surface of which had been pre-treated to prevent the penetration of organic solvents, and is dried. By means of a corona discharge, the coated paper is provided with a negative electrostatic charge, then exposed under a positive master to the light of a 100 watt electric bulb, and finally contacted in known manner with a developer consisting of a mixture of a toner and a carrier. As the carrier, glass balls, iron powder and other inorganic substances may be used. The toner consists of a resincarbon black mixture or of colored resins having particle sizes from 0.1 to 100/L. An image corresponding to the master is produced which is fixed by slight heating and excels by good contrast effect.

If, in the process just described, a transparent support is used, e.g. a cellulose acetate film or transparent paper, the image obtained by the electrophotographic process may be used for the production of further copies on similar or other light-sensitive layers.

EXAMPLE 2 1 part by weight of 2,5-bis-[4-di-n-propylaminophenyl (1)]-1,3,4thiodiazole (corresponding to Formula 2), 1.5 parts by weight of a ketone resin, having a softening range of 76-82 C. and an acid number of 0, and 0.005 part by Weight of Brilliant Green are dissolved in 20 parts by volume of ethylene glycol monomethylether and the solution is coated onto an aluminum-laminated paper base. After evaporation of the solvent, there remains on the aluminum surface a tightly adhering layer. After applying a negative charge by means of a corona discharge, the paper is exposed for 10 seconds, under a positive master, to the light of a 100 watt incandescent lamp at a distance of 30 cm. The layer is then contacted with a developer as described in Example 1. An image corresponding to the master is produced which is fixed with trichloroethylene vapors.

Example 3 In 100 parts by volume of ethyleneglycol monomethyl ether there are dissolved 5 parts by weight of 2-[4'-methoxy-phenyl-(1')]-5-[4" di n propyl amino phenyl- (1")]-1,3,4-thiodiazole (corresponding to Formula 9), 5 parts by weight of a styrene copolymeride containing carbonyl groups, having a decomposition range of 200 to 210 C. and a specific gravity of l.15l.16 (Lustrex 820), and 0.01 part by weight of Rhodamine B extra. This solution is used for coating a mechanically brushed aluminum foil, the depth of brushing averaging 5 to 7p. After evaporation of the solvent, a layer remains which adheres firmly to the foil surface and has a thickness of 4.7,u. The electrocopying material thus produced is negatively charged and then exposed at stop 9 for 20 to 30 seconds, depending on the picture scale, in the plate holder of a reproduction camera provided with an inverting prism. The light source used consists of 8 Nitraphot incandescent lamps of 500 watts each. A book page printed on both sides is used as the master. Without the use of a magnetic brush, areas of DIN A4 size on these layers can be uniformly developed by means of a developer powder.

The developer powder used may, e.g. be a mixture of kieselguhr and a toner which cOnsists of a low melting point polystyrene-colophony mixture with carbon black and advantageously also spirit-soluble nigrosin added as dyestutf. After dusting over with this toner mixture, the electrostatic image is fixed within 30 seconds by heating to 160-170 C. The imaged electrophotographic material thus produced may be converted into a printing plate by wiping over with a solution containing 40 percent by weight of methanol, 10 percent of glycerine, 45 percent of glycol, and 5 percent of sodium silicate. By this treatment, the areas not covered by the toner are dissolved away and become hydrophilic, while the areas from which printing is to be effected, the so-called image areas,

accept greasy ink, so that printing can be begun after the printing plate thus obtained has been set up in an offset rinting apparatus. Very good prints are obtained.

Example 4 1 part by weight of 2-phenyl-5-[4'-diethylamino-phenyl- (1')]-1,3,4-thiodiazole (corresponding to Formula 7), 1 part by weight of a resin-modified maleic acid resin (Beckacite K), and 0.006 part by weight of Eosin S are dissolved in 30 parts by weight of chloroform; the solution is coated onto a paper which is impermeable to solvents. After evaporation of the solvent, the layer which remains adheres firmly to the paper surface. For the preparation of an image, further processing is as in Example 1, and when a positive master is used, a positive image is obtained which is fixed as described in Example 1.

Example 5 The procedure described in Example 1 is followed but, after drying, the layer is positively charged and exposed under a negative master. After developing and fixing as in Example 1, a good positive print is obtained.

Example 6 0.6 partby weight of 2-[pyridyl-(4)]-5-[4"-diethylamino-phenyl-(1")]-l,3,4-thiodiazole (corresponding to Formula 16), 0.4 part by weight of 2,5-bis-[4'-isoamylamino-phenyl-(1)]-1,3,4-thiodiazole (corresponding to Formula 5) and 0.4 part by weight of 2-[4'-chloropheny1-(1)] 5 [4" diethylamino-phenyl-(1")]-1,3,4- thioiazole (corresponding to Formula 8) are dissolved in 40 parts by volume of chloroform and the solution is applied to a brushed aluminum foil. After evaporation of the solvent, a layer remains which adheres firmly to the foil surface. Further procedure is as in Example 1, and an image corresponding to the master is obtained on the aluminum foil which, after dusting over with a developer as described in Example 1, is fixed by heating. The aluminum foil thus provided with an image may be converted into a printing plate by Wiping over the image side of the aluminum foil with 80 percent alcohol, rinsing with Water, and rubbing with greasy ink and one percent phosphoric acid. A printing plate corresponding to the master used is thus obtained from which prints can be obtained after setting it up in an offset apparatus.

Example 7 1 part by weight of 2-[4'-methoxy-phenyl-(1)]-5-[4"- dimethyl-amino-phenyl-(1")]-1,3,4 thiodiazole (corresponding to Formula 10), 3 parts by weight of 2-[2'- tolyl-(1')]-5-[4-diethylamino-phenyl-( 1")] 1,3,4-thiodiazole (corresponding to Formula 13), and 5 parts by weight of a phenol-formaldehyde resin, having a softening range of 108118 C. (Alnovol K429), and 0.008 part by weight of Patent Blue AE are dissolved in a mixture consisting of 50 parts by volume of benzene and 50 parts by volume of chloroform. A paper which has been pretreated to prevent the penetration of solvents is coated with this solution. On this paper, direct images are produced by the electrophotographic process as described in Example 1. The layers are very light-sensitive so that images may be produced by the episcopic process from masters printed on both sides.

Example 8 A mixture of 2 parts by weight of 2-[naphthyl-(l)]-5- [4"-diethylamino-phenyl(1)]-1,3,4-thiodiazole, 2 parts by weight of 2,5-bis-[4'-diethylamino-phenyl-(1)]-1,3,4- oxadiazole, and 5 parts by weight of a ketone resin (Kunstharz AP) is dissolved, with 0.003 part by weight of methyl violet, in parts by volume of ethylene glycol monomethyl ether, and the solution is coated onto an aluminum-laminated paper base. After evaporation of the solvent, a layer remains which adheres firmly to the aluminum surface. The layer is positively charged by means of a corona discharge and then exposed under a positive master. The developer used consists of a colored resin-carbon'black mixture and tiny glass balls covered with resin. A positive copy is obtained.

It will be obvious to those skilled in the art that many modifications may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications.

What is claimed is:

1. An electrcphotographic material comprising a conductive base material and a photoconductive insulating layer thereon, the latter comprising a compound having the formula N-N t t \S/ Rz in which R and R are selected from the group consisting of hydrogen, aliphatic hydrocarbon groups, saturated carbocyclic groups, and heterocyclic groups, and R is selected from the group consisting of aryl and hetero-' cyclic groups. I

-2. An electrophotographic material according to claim 1 in which the insulating layer contains a resin.

3. An electrophotographic material according to claim 1 in which the insulating layer containsa dyestuff sensitizer.

'4. An electrophot-ographic material according to claim 1 in which the base material is metal.

5. An electrophot-ographic material according to claim 1 in which the base material is aluminum.

6. An electrophotographic material according to claim 1 in which the base material is paper.

7. An electrophot-ographic material according to claim 1 in which the base material is plastic.

8. An elect-rophotographic material comprising a conductive base material and a photoconductive insulating layer thereon, the latter comprising a compound having the formula 1 t? (CninntG- (IQ-Ma net 9. An electrophotographic material comprising a conductive base material and a'photoconductive insulating layer thereon, the latter comprising a compound having the formula CHHmNAQ -ii (IQ-Nflhfir):

10. An electrophotographic material comprising a conductive base material and a photoconductive insulating layer thereon, the latter comprising a compound having the formula crno-@o o-Q-mon-n):

11. An elec-trc-photographic material comprising a conductive base material and a photoconductive insulating layer thereon, the latter comprising a com-pound having the formula 13. An electrophotographic material comprising a conductive base material and a photoconductive insulating 10 layer thereon, the latter comprising a compound having the formula I 14. -An electrophotographic material comprising a conductive base material and a photoconductive insulating layer thereon, the latter comprising a compound having the formula 15. An electrophotographic material comprising a con ductive base material and a photoconductive insulating layer thereon, the latter comprising a compound having the formula the formula II I] 17. An electrophotographic material comprising a conductive base material and a photoconductive insulating layer thereon, the latter comprising a compound having the formula 18. A method of making an electrophotographic material which comprises coating a conductive base material with a solution comprising a photoconductive compound and volatilizing the solvent, the compound having the formula -in which R and R are selected from the group consisting of hydrogen, aliphatic hydrocarbon groups, saturated carbocyclic groups, and heterocyclic groups, and R is selected from the group consisting of aryl and heterocyclic groups.

19. A method according to claim 18 in which the base material is aluminum.

20. A photographic reproduction process which comprises exposing an electrostatically charged, supported photoconductive insulating layer to light under a master and developing the resulting image with an electroscopic material, the photoconductive layer comprising a compound having the formula in which R and R are selected from the group consisting of hydrogen, aliphatic hydrocarbon groups, saturated carbocyclic groups, and heterocyclic groups, and R is selected from the group consisting of aryl and heterocyclic groups.

21. A photographic reproduction process according to claim 20 in which the insulating layer contains a resin.

22. A photographic reproduction process according to 1 I claim in which the insulating layer contains a dyestulf sensitizer.

23. A photographic reproduction process according to claim 20 in which the support is metal.

24. A photographic reproduction process according to claim 20 in which the support is aluminum.

25. A photographic reproduction process according to claim 20 in which the support is paper.-

26. A photographic reproduction process according'to claim 20 in which the support is plastic.

27. A photographic reproduction process which comprises exposing an electrostatically charged, supported photoconductive insulating layer to light under a master and developing the resulting image with an electroscopic material, the photoconductive layer comprising a compound having the formula 28. A photographic reproduction process which com prises exposing an electrostatically charged, supported photoconductive insulating layer to light under a master and developing the resulting image with an electroscopic material, the photoconductive layer comprising a compound having the formula i ""ii mummQ-o o-Q-Nmutm 29. A photographic reproduction process which comprises exposing an electrostatically charged, supported photoconductive insulating layer to light under a master and developing the resulting image with an electroscopic material, the photoconductive layer comprising a compound having the formula 3 i i orno-{ -c oQ-Nwunn 30. A photographic reproduction process which comprises exposing an electrostatically charged, supported photoconductive insulating layer to light under a master and developing the resulting image with an electroscopic material, the photoconductive layer comprising a compound having the formula 31. A photographic reproduction process which comprises exposing an electrostatically charged, supported photoconductive insulating layer to light under a master and developing the resulting image with an electroscopic material, the photoconductive layer comprising a compound having the formula 33. A photographic reproduction process which comprises exposing an electrostatically charged, supported photoconductive insulating layer to light under a master and developing the resulting image with an electroscopic material, the photoconductive layer comprising a com- NN H H C pound having the formula o S o Q-mcnrm 34. A photographic reproduction process which comprises exposing an electrostatically charged, supported photoconductive insulating layer to light under a master and developing the resulting image with an electroscopic material, the photoconductive layer comprising a compound having the formula 35. A photographic reproduction process which comprises exposing an electrostatically charged, supported photoconductive insulating layer to light under a master and developing the resulting image with an electroscopic material, the photoconductive layer comprising a compound having the formula 36. A photographic reproduction process which comprises exposing an electrostatically charged, supported photoconductive insulating layer to light under a master and developing the resulting image with an electroscopic material, the photoconductive layer comprising a compound having the formula in which R and R are selected from the group consisting of hydrogen, aliphatic hydrocarbon groups, saturated carbocyclic groups, and heterocyclic groups, and R is selected from the group consisting of aryl and hetero cyclic groups.

38. A process according to claim 37 in which the insulating layer contains a resin.

39. A process according to claim 37 in which the insulating layer contains a dyestuff sensitizer.

40. A process according to claim 37 in which the support is metal.

41. A process according to claim 37 in which the support is aluminum.

42. A process according to claim 37 in which the sup port is paper.

43. A process according to claim 37 in which the support is plastic.

44. A process for making a printing plate which comprises exposing an electrostatically charged, supported photoconductive insulating layer to light under a master, developing the resulting image with an electroscopic material, fixing the image, and hydrophilizing the image-free areas, the photoconductive layer comprising a compound having the formula l l waramQ- Q-moan) 45. A process for making a printing plate which comprises exposing an electrostatically charged, supported photoconductive insulating layer to light under a master, developing the resulting image with an electroscopic material, fixing the image, and hydrophilizing the image-free areas, the photoconductive layer comprising a compound having the formula 46. A process for making a printing plate which com prises exposing an electrostatically charged, supported photoconductive insulating layer to light under a master, developing the resulting image with an electroscopic material, fixing the image, and hydrophilizing the image-free areas, the photoconductive layer comprising a compound having the formula 47. A process for making a printing plate which comprises exposing an electrostatically charged, supported photoconductive insulating layer to light under a master, developing the resulting image with an electroscopic material, fixing the image, and hydrophilizing the image-free areas, the photoconductive layer comprising a compound having the formula 48. A process for making a printing plate which comprises exposing an electrostatically charged, supported photoconductive insulating layer to light under a master, developing the resulting image with an electroscopic material, fixing the image, and hydrophilizing the image-free areas, the photoconductive layer comprising a compound having the formula 49. A process for making a printing plate which comprises exposing an electrostatically charged, supported photoconductive insulating layer to light under a master, developing the resulting image with an electroscopic material, fixing the image, and hydrophilizing the image-free areas, the photoconductive layer comprising a compound having the formula 50. A process for making a printing plate which comprises exposing an electrostatically charged, supported photoconductive insulating layer to light under a master, developing the resulting image with an electroscopic material, fixing the image, and hydrophilizing the image-free areas, the photoconductive layer comprising a compound having the formula 51. A process for making a printing plate which comprises exposing an electrostatically charged, supported photoconductive insulating layer to light under a master, developing the resulting image with an electroscopic material, fixing the image, and hydrophilizing the image-free areas, the photoconductive layer comprising a compound having the formula 52. A process for making a printing plate which comprises exposing an electrostatically charged, supported photoconductive insulating layer to light under a master, developing the resulting image with an electroscopic material, fixing the image, and hydrophilizing the image-free areas, the photoconductive layer comprising a compound having the formula 53. A process for making a printing plate which com prises exposing an electrostatically charged, supported photoconductive insulating layer to light under a master,

developing the resulting image with an electroscopic material, fixing the image, and hydrophilizing the image-free areas, the photoconductive layer comprising a compound having the formula FOREIGN PATENTS 558,630 12/1957 Belgium.

NORMAN G. TORCHIN, Primary Examiner.

R. E. MARTIN, Assistant Examiner. 

1. AN ELECTROPHOTOGRAPHIC MATERIAL COMPRISING A CONDUCTIVE BASE MATERIAL AND A PHOTOCONDUCTIVE INSULATING LAYER THEREON, THE LATTER COMPRISING A COMPOUND HAVING THE FORMULA 